Chroma Key allows you to remove the background from your webcam feed. To do this, go into your settings.

Look for the gear icon near the top of the screen.

Select a webcam from your Devices tab.

Make sure you have a webcam plugged in.

Once your webcam is set up, go back to the Studio tab and start editing an overlay with a webcam source in it.

The editor opens via this icon next to the viewport.

Click on your Camera Source inside the overlay editor. From the Properties sidebar you can enable or disable your webcam's Chroma Key, and set which color it's removing from the background.

Most users have themselves against a green background for this.